1. Field:
This invention is related generally to liquid level monitoring apparatus. More particularly, the invention is directed to a monitoring means for use in verifying the level of oil or other liquid in a crankcase or other reservoir, which crankcase or reservoir is located remote from the access openings.
2. State of the Art:
In conventional practice, an internal combustion engine includes a crankcase or oil supply reservoir whose contents are monitored by means of a bladed dipstick assembly. This dipstick assembly generally includes an open-ended, continuous, tubular conduit which extends from an easily accessed location remote from the crankcase or oil supply reservoir, which typically is located in the lower regions of the engine assembly. Inserted within the conduit is a thin elongated blade which is dimensioned to slide through the conduit and thereby access the oil reservoir. The end portion of the dipstick which extends into the reservoir contains a series of etched markings which function as reference points.
To verify the oil reservoir level, the dipstick blade is inserted into the conduit such that an abutment member positioned proximate the blade's proximal end is brought into contact with the accessible end of the conduit so as to preclude further insertion of the blade into the conduit. In this fully inserted position, the distal end of the blade is positioned at a predetermined depth within the oil reservoir; i.e., the etched markings on the blade are positioned at a predetermined depth. The dipstick is dimensioned such that in its fully inserted position within the conduit, the distal, etched end of the blade is immersed in the oil extant within the reservoir.
The depth of the blade's penetration into the oil is a matter of design choice. To measure the oil level, the blade of the dipstick, being coated with oil, is removed from its conduit housing. The uppermost level of the coating of oil on the blade is then referenced against the etched markings on the blade. Since the blade was inserted to a predetermined depth within the reservoir, the relationship of the oil-coated level on the blade with the etched markings permits the oil level to be determined without actual visual inspection of that oil level.
As may be noted, the conventional monitoring practice utilizing a dipstick has serious drawbacks. Owing to the motion of the vehicle, the oil within the crankcase or reservoir is in constant motion. The dipstick is typically retained in its fully inserted position within the conduit during normal operation of the automobile. The motion of the oil tends to cause the oil to splash the dipstick, thereby leaving an oil coating on it which is not reflective of the true level of oil in the oil reservoir. Because of the viscosity of oil, this splashed oil coating will remain for a sufficient time that any monitoring of the oil level soon after driving of the automobile may be misleading. This phenomena is generaly addressed by a motorist by removing the dipstick prior to taking the reading and cleaning any oil residue from the blade tip. The blade is then reinserted and then removed again in order to obtain a valid reading. This process involves a considerable risk that the motorist will be soiled by the oil residue on the blade during the process.
The oil to be monitored, if recently changed, is substantially clear. The absense of color hinders attempts to compare the oil level against the markings on the dipstick blade. Reading a dipstick coated with clean oil at night or under conditions of poor lighting is difficult.
Typically, the conventional monitoring practice is time-consuming and subjects a motorist to the likelihood of being soiled by contact with various portions of the engine or, alternately, the oil removed from the reservoir by the dipstick. This inconvenience discourages many motorists from regularly checking the engine oil level of their vehicles. Such failure often leads to expensive and extensive engine damage.
Prior efforts in the art have attempted to simplify the monitoring process. The problems caused by removing the dipstick from its housing was addressed in U.S. Pat. No. 2,660,058 to Vogt. Vogt discloses a conduit-housed indicator which operates to lift a representative sample of oil to a position which permits a visual examination of the sample in relationship with a series of reference indicia. The indicator is never entirely removed from its conduit housing.
Various devices have been described which utilize induced pneumatic pressure variances to effect a displacement of an indicator fluid within a manometer or other differential pressure indicator. Representative of these devices are those proposed in U.S. Pat. No. 3,834,236 to Durin; U.S. Pat. No. 1,792,754 to Myers; U.S. Pat. No. 3,972,234 to Osojnak; U.S. Pat. No. 4,235,186 to Frobose; U.S. Pat. No. 1,241,384 to Hueber; U.S. Pat. No. 1,368,187 to Murphy; U.S. Pat. No. 3,935,835 to Rinck; and U.S. Pat. No. 4,055,898 to Bruan, et al.